On theater stages and TV studios, horizontal pipe battens or trusses are utilized to suspend lighting, scenery, drapery and other equipment. These battens usually consist of pipes joined together with sleeves to form the desired length batten. Typically, these battens can be 50 ft. or more in length. To support heavy loads or where suspension points are spaced 15 ft. to 30 ft. apart, battens are fabricated in either ladder, triangular or box truss forms. Aluminum pipe or tubing is utilized to reduce the weight of the batten, when weight is an important factor.
Battens often need to be easily lowered for changing and servicing the suspended equipment. Currently, numerous elevating or hoisting systems are available for supporting, raising and lowering battens. One of the most common and least expensive batten elevating systems is a counterweighted carriage which includes a moveable counterweight for counterbalancing the batten and equipment supported thereon.
Another common elevating or hoisting system uses a winch to raise and lower the battens. Usually hand or electric operated winches are used to raise or lower the batten. Occasionally, in other more expensive installations, a hydraulic or pneumatic motorized winch or cylinder device is used to raise and lower the batten. The batten in a winch type elevating system is typically connected to the winch via a plurality of cables. Specifically, the cables are attached at one end to the batten and then run over pulleys located at the stage ceiling and then directed downwardly through multi-groove pulleys on the side walls, and finally connected at their other ends to the winch.
Except in the case of chain winches, usually a single winch operates each of the battens. Battens rigged with chain winches, on the other hand, usually require multiple winches since it is not practical to run multiple heavy chains across the ceiling. Chain winches are either suspended from the ceiling or mounted directly to the batten. Hand winches are almost always mounted on the wall, while electric winches, with one or more cable drums, can be mounted almost anywhere. Counterweight systems and hydraulic or pneumatic winch systems are all typically located at the side walls.
Many elevating systems have one or two locking devices and at least one form of overload limiting device. One example of an overload limiting device is a counterweight carriage system which includes a carriage holding a weight which is attached to the pipe batten by multiple cables. These cables run from the top of the counterweight to the batten over multiple sheaves and a head block. The size or height of the carriage limits the amount of counterbalancing load, and therefore acts as the weight overload limit. In a counterweight system, the locking device would consist of a hand operating rope that is attached at one end to the top of the counterweight and then run over a head block, down to the stage, through a hand rope lock for locking the counterweight in place, and then around a floor block and back up to the bottom of the counterweight. The hand rope lock locks the rope when either batten or counterweight loads are being changed and rebalanced, and locks the loads when not moving.
In a sandbag counterweight system, the locking device is merely a rope tied off to a stage mounted pin rail, while the overload limit is regulated by the size of the sandbag. In this rigging design, however, any number of additional bags can be added to the set of rope lines, and thereby exceed the safe limit of the suspension ropes and defeat the overload limiting feature.
Hand operated winches typically have worm gear drives with about a 50 to 1 gear ratio, and they use friction as their locking device. The strength of the person turning the operating handle of the winch acts as the overload limiting system. A second safety lock for a worm gear winch is provided by tying off its operating handle. However, these winches will occasionally free run when heavily loaded and will then dangerously drop their suspended load. Other types of hand winches use a ratchet lock, but again these winches are also susceptible to free running when they are heavily loaded and hand operated. In all hand operated winch designs, multiple cables from the batten terminate to a clew plate which is then attached to a single cable wrapped around the winch drum. Thus, the load is in effect suspended by a single cable and single winch, either of which when they fail will completely drop the load.
Motorized winches can be mounted either on a wall, a batten (self-climbing) or a grid (ceiling beam). Typically, motorized winches use abruptly stopping electric friction brakes and worm gear reducers for their load locking device, and (at the least) their horsepower rating to act as their overload limit. Some more advanced designs incorporate limit switches that sense pulley motion over which the supporting cables have been run to detect weight overloads and underloads. Expensive winch designs, with electronic drives, monitor the back EMF for excessive torque to detect overloads. Motorized winch systems also utilize end of travel limit switches to prevent excessive travel in either direction and thermal overloads to detect motor overheating. Most motorized winch designs do not include any form of smooth ramped starting and stopping to prevent damage to the lamp filaments when raising and lowering lighting battens as it is very expensive.
In professional theater installations, computer controlled drives use variable speed drives to control stepper, AC & DC motors, with and without some form of position feedback. These systems are usually too complex and too expensive for most theater rigging installations.
Only in professional theater scenery operation, where the rapid operation of set pieces is necessary for a production, is the expense of multiple drive motors with multiple variable speed drive controls incorporated. These systems often utilize computer controls, servo feedback systems or some form of shaft encoder to monitor and control the loads. For the average theater or studio, maintenance of these expensive professional elevating systems is too complex. Moreover, these complex elevating systems are difficult and dangerous to operate, except by trained technicians or engineers.
One typical motorized winch design is a self-contained, self-climbing design. It uses a single drive motor, two flat cable drums, a single worm gear reducer with a 58:1 ratio, and weight detecting limit switches. The weight detecting limit switches are mounted adjacent to spring loaded pulleys which have the two suspension cables run under them. They detect weight overload and underload on the two cables when they are tilted in and out from varying loads on the cables. The cables wind upon themselves on their respective drums and the load travels perfectly vertically. This type of system is suitable for short 10 ft. battens which are typically used in TV studios. However, they are unsafe since either a single cable, drive, or gearbox failure would cause the entire load to drop down. Most other types of winch systems use more than two suspension cables attached to a single batten for safety.
Another motorized winch design is a common drive shaft ceiling mount type which uses one large ceiling mounted winch drive system connected to a long drive shaft with a plurality of cable drums clamped to the underside of the ceiling I-beams. Each cable drum is located at a cable drop point. This design adds additional cables to support the pipe batten and thus is safer than the single cable support design and the two cable support design. However, load locking in this type of winch relies upon a single common shaft with multiple flexible couplings, driven by a single gearbox and locked by a single gearbox and brake. The winch is usually inaccessibly mounted at the ceiling and the load moves horizontally during raising and lowering. End of travel limit switches, located at the winch, prevent overtravel but there is no underload protection should the batten hit an obstruction. Starting and stopping is abrupt since an electric brake mounted on the drive motor, must be used to support the load.
There is a self-climbing winch design, in which the horizontal travel of the batten during raising and lowering of the batten is eliminated by using a single large motorized winch mounted on wheels and tracking in a square box truss batten. In this design, the winch rotates a common shaft which drives multiple cable drums mounted across the batten. The entire mechanism travels horizontally within the box batten during drum rotation to eliminate misalignment of the suspension cables, and thereby provide a vertical travel of the batten as the cables are wound up. Again, the safety of multiple suspension points is provided. However, only a single gearbox and brake system is utilized for supporting the load. Also starting and stopping are abrupt. This makes this drive less than satisfactory for a lighting batten.
It is common for hand operated winches to run and drop their load or for the winches to pull from their wall mountings causing their loads to crash onto the stage. Electric brake winches used in all forms of rigging systems often fail as well as all forms of rigging systems with only one or two primary suspension lines to a batten. In systems using single drive motors and single end of travel up and end of travel down limit switches, it is not uncommon to have a single switch failure destroy the entire system.
Rope lines in manila rope sets regularly fail due to damaged ropes or overloads. Counterweighted carriage systems are often carelessly operated or improperly counterweighted, and brake free from their rope locks and crash to the stage. In the older cast iron type counterweight carriage systems, they have broken and dropped their loads causing an up-down crash. In other words, first the counterweight crashes to the stage typically because too many lights were removed from the batten without lightening the counterweight. Then, after the counterweight crashes and brakes its bottom weight holding casting, the lighting pipe comes down and it crashes the stage.
Motorized drive systems mounted to the ceiling grid of stages, even when accessible, have failed due to the difficulty in servicing them as they cannot be easily removed or repaired, unless the entire batten load is removed.
In view of the above, it is apparent that there exists a need for an elevating system which will overcome the problems of the prior art, and which is safe to operate and inexpensive to manufacture. This invention addresses this need in the art along with other needs which will become apparent to those skilled in the art once given this disclosure.